It's impossible to know for sure how non-RCV elections would have played out if RCV were used, especially since RCV changes how people run. The NYC dem primary was a great example of this with all the cross-endorsements that happened. And there totally would have been a "don't rank Vallas" push.
Lori Lightfoot's supporters would have been pushing don't rank Vallas while mostly everyone else would have been pushing "don't rank Lightfoot" A lot of white people ignored complaints about Vallas during the first round of voting due them coming from Lightfoot's campaign speaking out against him.
Not everyone is going to research all the candidates. Vallas was the only white candidate in the race. A lot of white people were biased in his favor during the 1st round of voting. It wasn't until there were 2 people in the race that some of them paid enough attention & learned how bad Vallas is.
The same goes for the older people who didn't do research during the first round of voting and only knew Vallas from him running as Democratic nominee for lieutenant governor in 2014 or governor in 2002. It wasn't until the second round of voting that they learned about how bad Vallas is.